Experiments on Enzyme Activity

Enzymes are proteins that catalyze biochemical reactions. Catalysts work by lowering the activation energy of chemical reactions, and enzymes play a major role in biochemical processes in all organisms. Enzyme activity is influenced by many factors, both biotic and abiotic. Factors that affect enzyme activity include temperature, pH, substrate concentration and enzyme concentration. The influence of these can be observed in the laboratory.

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All enzymes have an optimum temperature at which they function at the maximum reaction velocity. As molecular motion increases with increasing temperature, enzyme molecules encounter substrate molecules more frequently. But at a certain point, increasing temperature may cause enzyme structure to denature. Amylase is an enzyme that catalyzes the breakdown of starch. You can measure the effects of temperature on amylase activity. Set up a series of test tubes kept at varying temperatures and add a starch solution to each. Add a solution of amylase to each. Let the tubes sit for 10 minutes and add iodine to test for the presence of starch in each tube. The iodine will react with the remaining starch and turn a dark purple color.

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pH is an expression of the hydrogen ion concentration in a solution. Acidic or alkaline pH can alter the three-dimensional structure of an enzyme, changing the shape of the active site and preventing binding of the enzyme to the substrate. Measure the effects of pH on amylase activity by setting up a series of test tubes with varying pH levels. Add a solution of amylase to each. Let the tubes sit for 10 minutes and test with iodine.

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Biochemical reactions can proceed without enzymes, but they will do so very slowly. The rate of a biochemical reaction is directly proportional to the amount of enzyme present. If the enzyme is present in amounts excess to the substrate, the reaction will proceed at the maximum rate. Catalase is an enzyme that catalyzes the breakdown of hydrogen peroxide to oxygen and water. You can measure the effect of catalase concentration on catalase activity by adding variable amounts of yeast, an organism that produces catalase, to test tubes. Then add the same amount of hydrogen peroxide to each test tube. Then measure the amount of oxygen gas produced with a syringe.

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Substrate concentrations also influence reaction rate. At lower substrate concentrations, the reaction rate is proportional to the substrate concentration. Once substrate concentration exceeds enzyme concentration, there are no more enzyme active sites for the substrate molecules to bind to. You can measure the effect of hydrogen peroxide concentration on catalase activity by adding different concentrations of hydrogen peroxide to several test tubes. Add the same amount of yeast to each test tube, and measure the amount of oxygen gas produced.